1. Field of the Invention
The present invention relates to a technology for forming an image in an image forming apparatus.
2. Description of the Related Art
An image forming apparatus, such as a laser printer, employing an electrophotographic system has a problem that an image forming condition such as an image density and an image gradation changes due to change in environment such as temperature and humidity at an area where the image forming apparatus is installed or changes with time. In a conventional image forming apparatus, a patch pattern including a plurality of patches is formed at predetermined timing for providing information necessary for adjusting the image forming condition. A sensor detects the patch pattern and the image forming condition is adjusted based on a result of the detection. However, if the image forming condition is adjusted during a print operation, the print operation needs to be interrupted from the time when formation of the patch pattern is started to the time when detection of the patch pattern ends, which causes downtime of the image forming apparatus thereby reducing productivity of the image forming apparatus.
To solve such a problem, Japanese Patent Application Laid-open No. 2007-133356 discloses an image forming apparatus in which a specific area for forming a patch pattern (hereinafter, patch-pattern forming area) is arranged on an intermediate transfer belt in advance. The intermediate transfer belt is not in contact with a secondary-transfer unit at the patch-pattern forming area and a patch pattern formed at the patch-pattern forming area is detected. With this method, it is possible to reduce time required for detecting the patch pattern.
However, in the above method, because the patch pattern is formed on the intermediate transfer belt such that the patch pattern is arranged in parallel to an image to be transferred onto a recording medium, the size of the image forming apparatus is increased.